The document evaluates the effect of temperature on polyethylene terephthalate (PET)-coated electrolytic chromium-coated steel plates immersed in an acetic-acetate medium. Samples with flat and rippled walls were immersed at 40, 60, and 80°C. Raman spectroscopy showed the temperature had no effect on acid absorption by the PET coating. The rippled samples had greater amorphousness due to mechanical deformation during manufacturing. Higher temperatures slightly reduced crystallinity near the steel interface but did not compromise the steel plate. The medium increased failures and deterioration of manufacturing defects on the PET surface. A combination of techniques characterized the PET coating's protective capacity on the steel plates.

1. EFFECT OF TEMPERATURE ON POLYETHYLENE
TERAPHTHALATE COATED ECCS PLATES IN
ACETIC-ACETATE MEDIUM.
E.Zumelzu(1), F. Rull(2), C. Ortega(3), C. Cabezas(4)
(1) Instituto de Materiales y Procesos Termomecánicos, Universidad Austral de
Chile, Casilla 567, Valdivia, Chile, email: ezumelzu@uach.cl;
(2) Dpto. Física de la Materia Condensada, Universidad de Valladolid, Spain;
(3) Escuela de Mecánica, Facultad de Ciencias de Ingeniería, Universidad Austral de
Chile, Valdivia, Chile;
(4) Instituto de Química, Universidad Austral de Chile, Valdivia, Chile.

2. INTRODUCTION
• The metal-polymers plates are intended to replace the
conventional steel containers coated with sanitary lacquers, due
to the minimum emission of solvents and chemical elements
when compared with the traditional lacquers.
• The electrolytic-chromium coated steels (ECCS), surface-
protected by a polyethylene teraphthalate (PET) co-rolled layer,
are multifunctional advanced materials.
• The polymer coated sheets can undergo damage during rolling
and forming resulting in fracture, features that are of
considerable importance to determine the formability limits of this
multilayer material.
• In other recent works, was possible to determine that after nine
months of exposure the PET suffered significant degradation by
the acetic-acetate medium, limiting the protection capacity of the
coating and its useful life in containers.

3. OBJETIVES
• The present study is aimed at evaluating under controlled experimental
conditions the effect of temperature on PET-coated ECCS plates in an acetic-
acetate medium, simulating the thermal shock conditions occurring during food
canning.
• A later evaluation of the system through electrochemical polarization of the
samples, allows as a whole the determination of the occurrence of PET
degradation by evidencing the coating detachment, which limits the functionality
of the protective polymer.
• The application of a combination of macro and micro techniques in order to
characterize the material performance, such as vibrational spectroscopy and
electron microscopy, can determine the suitability of the methods employed to
study these knowledge-intensive material composites.

4. MATERIALS AND METHODS
The ECCS plate is coated with a fine, 0.02 µm thick layer of chromium
oxide and metallic chromium that protects the steel from the
environment and at the same time serves as a substrate, facilitating the
adherence of the PET polymer to the material.
(Corus)

5. MATERIALS AND METHODS
Table 1. Chemical composition of the alloying elements of the ECCS plate
participating in the alloy iron.
Chemical Composition % W t
%C %Mn %P %Sº %Si %Al N(ppm)
ECCS 0.074 0.260 0.021 0.016 0.012 0.032 45

6. MATERIALS AND METHODS
• In this study, 90 coupons of PET-coated ECCS plates, half of them having
flat walls and the other half having crippled walls, mechanically formed by
pressure, and obtained from new containers.
• Were prepared. 0.1-m immersion trials in an acetic-acetate medium at
room temperature and at ph 3.85, representative of fish and shellfish foods,
in an open system at 40, 60 and 80 °C, were performed.
• Some samples were submitted to a constant polarization electrochemical
test at 10 mV for 30 minutes in an acetic-acetate medium of the same
characteristics above mentioned.

7. MATERIALS AND METHODS
• The tested samples were analyzed by vibrational spectroscopy in order to
determine the occurrence of changes in the PET composition due to absorption
of the electrolyte, and changes at the structural level, in the crystallinity of the
polymer, signifying alterations in the functionality of the coating.
• This study employed a Raman device: Spectrometer Kaiser Holospec f/1.8i,
spectrum range 100-3800 cm-1, and a resolution of 4 cm-1. CCD Andor
DV420A-OE-130, laser melles-griot 0.5-lhp-151. He-Ne 632’8 nm. The samples
were macro analyzed by making the laser beam strike perpendicular to the
surface with a Raman of 785 nm.
• Also, cross-sections of the samples were micro analyzed parallel to the coating
by means of the Raman device at 633 nm, obtaining spectra every 10 µm at
different points starting from the PET surface until reaching the ECCS interface.

8. MATERIALS AND METHODS
• In addition, an ATR analysis with a 5-µ beam penetration to the PET
coating was performed in order to evaluate the events occurring on the
external surface, where the surface degradation of the coating starts.
• The samples were characterized by SEM and chemically microanalyzed
by X-ray dispersive energy, using a LEO 400 microscope and an Inca
microprobe, respectively.

9. RESULTS AND DISCUSSION
Figure 2. Comparison of Raman
Figure 1. Interpretation of the spectra for the flat (1) and rippled (2)
material substrates by Raman wall coupons at different
spectroscopy. temperatures in an acetic-acetate
medium.

10. Figure 3. Comparison of flat samples Figure 4. Comparison of rippled
submitted to electrochemical polarization samples submitted to electrochemical
at 40, 60, and 80 ºC. Micro Raman. polarization at 40, 60, and 80 ºC. Micro
Raman.

11. Figure 5. ATR spectra of the flat (1) Figure 6. Raman analysis of
and rippled (2) samples at different intensity variations in rippled wall
temperatures, showing no evidence sample at 80 °C, performed at
of surface damage on the PET. different points from the metallic
interface through the external PET
surface

12. Figure 8. Wave number cm-1
Figure 7. Raman spectrum of PET associated with the PET structure
associated with its chemical structure. crystallinity.

13. Figure 9. Morphology of PET coating Figure 10. EDAX chemical analysis of PET
on ECCS plate, mostly free of coating
defects. SEM

14. Figure 11. Flat sample tested at 40 Figure 12. Flat sample tested at 60
°C, showing a surface pore occurring °C, indicating surface detachment
during the PET manufacturing. SEM. defect caused by thermal shock
action. SEM.

15. Figure 13. Flat sample tested at 80 °C, Figure 14. Rippled sample tested at 40
exhibiting surface pore further ºC, showing globular microdetachment
degraded by acetic-acetate medium. of PET coating interacting with the
SEM. acetic-acetate medium and directing to
an increase in its volume and localized
surface propagation. SEM.

16. Figure 15. Rippled sample at 40 °C heating exposure, exhibiting
circular crack on the polymer surface resulting from
manufacturing, which increased in size as an effect of the
solution employed. SEM.0

17. CONCLUSIONS
Under the experimental conditions of study and considering the
techniques applied, the following conclusions can be drawn:
1.- The temperature had no effect on the acid absorption by the PET
coating of samples tested in an acetic-acetate medium, a fact
confirmed by the non significant spectral changes of the Raman and
ATR spectroscopies.
2.-The Raman spectra showed that the flat, PET-coated ECCS plate
samples evidenced greater crystallinity when compared with the
rippled samples, being the latter more amorphous, which is explained
by the mechanical deformation occurring during the manufacturing
process to produce food containers.

18. CONCLUSIONS
3.- The small variations detected by micro Raman in a parallel plane to the
coating thickness toward the metallic interface, and which were manifest
as reduced crystallinity changes in the polymer chains at the 1096 wave
number cm-1 spectral region, were a consequence of the mechanical
deformation of containers.
4.- A particular effect on the PET surface, and focused on the manufacturing
defects, was caused by the acetic-acetate medium which increased the
coating failures and induced deterioration spreading; however, without
compromising the steel plate.
5.- The combination of micro and macro Raman techniques, electron
microscopy, and electrochemical polarization allow to obtain convergent
results in the characterization and evaluation of the protective capacity of
PET’s on ECCS plates.

19. THANKS
ACKNOWLEDGMENTS
To Fondecyt Projects Nos. 1070375 and 7070062 (PICI) -Chile for their
financial support and the special contribution by Universidad Austral de
Chile.